A method for granulating a chemical substance having a melting point of 50-250° C. using a spray granulation apparatus is disclosed in Particulate Process and Technology, (supplemented revision), Chapter on Granulation, 3.3 Injection Granulation Apparatus, pages 43-50, Chemical Industry Publishing Co., Jan. 10, 1988. There is disclosed in a PCT International Patent Application Publication WO99/33555 a method for manufacturing a particulate chemical substance having a quite limited particle size distribution, which comprises the step of dropping a molten chemical from a nozzle plate, and blowing a cooling medium to dropping granules co-currently. The apparatus used in this method is commercially available from Goudsche Machinefabriek B. V. GMF Gouda, a company in the Netherlands, under the trademark Jet Priller. A published Japanese translation of PCT Application No. 2003-515598 describes that that apparatus can be used in granulation of phenothiazine, and in fact, the granulation using the same apparatus is carried out in Example 2.
As disclosed in Paragraph 0023 of published Japanese translation of PCT Application No. 2003-515598, the method employed in that document requires the steps of heating an inert gas such as nitrogen gas, and melting phenothiazine by using the heated gas at the time of melting it. Generally, a method for heating a gas possesses a problem in the viewpoint of energy consumption, compared with the case of heating a liquid. Furthermore, the method disclosed in that patent document, Paragraph 0025 thereof states that a vibration is given to molten chemical substance during its falling-down. There is described in a concrete manner no reason why the vibration is given at that stage in this document. However, it can be considered, based on the description of that paragraph, to form the molten substance, which is falling down from the nozzle into smaller droplets by giving a vibration at that stage. A similar description can be found in Claim 1 and Paragraph 0016 of a published Japanese translation of PCT Application No. 2004-502683. However, to make the molten substance into smaller droplets by giving vibration has a risk in that particulate chemical substances having a desired particle size distribution can not be obtained unless a vibration frequency is properly chosen.
In a process using as a raw material a large amount of a chemical substance which is solid at normal temperature, pneumatically transported substance is fed by air directly to process equipment via a pipe line at a prescribed feed rate using a prescribed volume of air. The properties required for the chemical substance to be pneumatically transported include an appropriate particle size distribution for ensuring delivery of a prescribed amount at a prescribed speed without leaving significant residues in the pipe, and sufficient strength preventing the particles from shredding into powder by colliding against the wall of pipes and the like. However, the methods disclosed in the above-mentioned patent documents are not said to produce particulate chemical substance having narrow particle size distribution and high hardness sufficient for use in pneumatic transportation processes.